VirtualTourist.com - Travel Guides, Maps, Photos, Forums, Deals, more:
"Worldwide Travel Guide. Tips, Reviews & Photos plus Hotels, Restaurants, Activities & More"
VirtualTourist.com may be the largest travel social website today, with over 700,000 members. In the previous 24 hours prior to this posting there were: 1,075 new travel tips posted; 2,034 new forum postings; 1,175 new page comments; 76 new travel deals; and 432 new members!
TripAdvisor.com is also a much visited social-like website (19 million visit per month), though with a much more narrow focus on accommodation reviews -- over 4 million user reviews, so far.